A key molecular property used for drug screening and design is the partition coefficient, measured by partitioning between an organic solvent and water, but more commonly calculated with algorithms based on octanol:water-derived hydrophobicity constants. However, it is the membrane:water partition coefficient that is more relevant to partitioning of drugs into cell membranes. In this project we propose to exploit Fluorosome Technology to efficiently determine true membrane:water partition coefficients of drugs. "Fluorosomes-intra" are fluorescently labeled membrane lipid bilayer vesicles that measure drug entry rates into the membrane. By varying the concentrations of both test drug and lipid bilayer, and analysis of data by equilibrium or kinetic algorithms, we will establish a simple, rapid partition coefficient assay with membranes containing lipids that exist in cell membranes. The assay will .be applicable to a wide range of molecules using standard spectrofluorimeters, and can be adapted to multiwell plate formats and robotics. The specific aims are: to develop the Fluorosome-intra assay conditions and mathematical data analysis methods for the measurement of membrane:water partition coefficients of drugs; to optimize the Fluorosome-intra technique for the routine measurement of membrane:water partition coefficients, and; to validate the results of Fluorosome-intra in comparison with published values of membrane:water partition coefficients of known drugs. We will acquire partition coefficients of an expanded set of test drugs with Fluorosome-intra for comparison and correlation with published results obtained by other techniques. Fluorosome-intra methodology has the capacity to greatly enhance our ability to determine and understand the partitioning of drugs and other small molecules between water and biomembranes. This project seeks to exploit features of the technique that will extend the tools available to the medicinal chemist and drug discovery scientist, and to take advantage of the high-throughput capacity of the technique. The implementation of the Fluorosome Technique to the acquisition of membrane:water partition coefficients will thus greatly facilitate drug discovery. [unreadable] [unreadable]